Git can use general proxy configuration on server,
such proxy configuration on ubuntu

export http_proxy=http://username:passwd@proxyserver:port

or use config git

[php]git config –global http.proxy http://username:passwd@proxyserver:port[/php]

if your proxy server doesnt need username and password simply write this command

[php]git config –global http.proxy http://proxyserver:port[/php]

now you can use git behind proxy

root@idsubuntu:/home/administrator# git clone http://github.com/Snorby/snorby.git
Cloning into snorby…
remote: Counting objects: 7232, done.
remote: Compressing objects: 100% (2159/2159), done.
remote: Total 7232 (delta 5054), reused 7081 (delta 4926)
Receiving objects: 100% (7232/7232), 4.83 MiB | 17 KiB/s, done.
Resolving deltas: 100% (5054/5054), done.